opencv-python- study notes eight (color space conversion)

1. color space conversion

There are more than 150 OpenCV color space conversion method. But we will study only the two most widely used, BGR↔Gray and BGR↔HSV, BGR and grayscale conversion using cv2.COLOR_BGR2GRAY,
BGR and HSV conversion using cv2.COLOR_BGR2HSV. In the HSV space, H represents hue / chroma range [0,179], S represents the saturation range [0,255], V represents luminance range [0,255]. But different values for different software

dst = cv.cvtColor( src, code[, dst[, dstCn]] )

parameter:

src: an input image: unsigned 8-bit, 16-bit unsigned (... CV_16UC), or a single-precision floating point.

code: conversion mode

dst: the same depth of the original image size of the output image. Can be omitted

dstCn: Standard image channel number, the default is 0, represented by the src and determined code.

Print all the code:

import cv2 as cv


flags = [i for i in dir(cv) if i.startswith('COLOR_')]
print(flags)

Function Description:

This function converts the input image from one color space to another color space.

 

For example

 

import matplotlib.pyplot as plt
import cv2

img_BGR = cv2.imread('2.jpg')  # BGR
plt.subplot(331), plt.imshow(img_BGR), plt.axis('off'), plt.title('BGR')

img_RGB = cv2.cvtColor(img_BGR, cv2.COLOR_BGR2RGB)
plt.subplot(332), plt.imshow(img_RGB), plt.axis('off'), plt.title('RGB')

img_GRAY = cv2.cvtColor(img_BGR, cv2.COLOR_BGR2GRAY)
plt.subplot(333), plt.imshow(img_GRAY), plt.axis('off'), plt.title('GRAY')

img_HSV = cv2.cvtColor(img_BGR, cv2.COLOR_BGR2HSV)
plt.subplot(334), plt.imshow(img_HSV), plt.axis('off'), plt.title('HSV')

img_YcrCb = cv2.cvtColor(img_BGR, cv2.COLOR_BGR2YCrCb)
plt.subplot(335), plt.imshow(img_YcrCb), plt.axis('off'), plt.title('YcrCb')

img_HLS = cv2.cvtColor(img_BGR, cv2.COLOR_BGR2HLS)
plt.subplot(336), plt.imshow(img_HLS), plt.axis('off'), plt.title('HLS')

img_XYZ = cv2.cvtColor(img_BGR, cv2.COLOR_BGR2XYZ)
plt.subplot(337), plt.imshow(img_XYZ), plt.axis('off'), plt.title('XYZ')

img_LAB = cv2.cvtColor(img_BGR, cv2.COLOR_BGR2LAB)
plt.subplot(338), plt.imshow(img_LAB), plt.axis('off'), plt.title('LAB')

img_YUV = cv2.cvtColor (img_BGR, cv2.COLOR_BGR2YUV) 
plt.subplot ( 339), plt.imshow (img_YUV), plt.axis ( ' OFF ' ), plt.title ( ' the YUV ' ) 
plt.show () 

CV2. imshow ( ' Gray ' , img_GRAY) 

K = cv2.waitKey (0)   # is always detected keyboard 
IF K == 27:   # press ESC exit 
    cv2.destroyAllWindows ()